Don't throw the SuspendedInvocationException when call the suspend() method of CXF continuation

Details

Description

Current CXF Continuation suspend implementation is based on throw SuspendedInvocationException, This implementation has a shortcoming which cannot call the other framework's async API after continuation suspend is called as Jetty7 does.
So I introduce a flag of Message.CONTINUATION_SUSPENDED to break out current interceptor chain as the SuspendedInvocation does, but It will make CXF continuation API more easy to use and it supports the Jetty7 continuation or Servlet3 suspend resume semantics.